docs: update code examples from gpt-5-nano to gpt-5.4-nano

[LeC-D]

Fixes #2716

What changed

Updated all documentation code examples and titles from gpt-5-nano to gpt-5.4-nano as requested in the issue.

Files updated:

• src/docs/src/AI.md — code example + section title
• src/docs/src/AI/chat.md — code examples + example title
• src/docs/src/index.md — code examples + section title + comment
• src/docs/src/examples.md — descriptions
• src/docs/src/supported-platforms.md — code example + comment
• src/docs/src/playground/examples/ai-chatgpt.html — model + comment
• src/docs/src/playground/examples/intro-chatgpt.html — model + comment
• src/docs/src/playground/examples/ai-gpt-vision.html — model + comment
• src/docs/src/playground/examples/intro-gpt-vision.html — model + comment

Not changed (intentionally):

• The line in chat.md documenting puter.ai.chat()'s default value remains gpt-5-nano, as the API default was not changed — only the examples were updated to showcase the newer model.

[CLAassistant]

All committers have signed the CLA.

[LeC-D]

Amended the commit author to LeC-D <leo.openc@gmail.com> and force-pushed — the previous commit had been authored with leo@openclaw.ai which wasn't linked to the GitHub account, triggering the CLA bot. The CLA status should now clear.

[LeC-D]

Rebased on upstream main (2026-03-27) to bring the branch back up to date.

[LeC-D]

Rebased on upstream main (2026-03-28) to bring the branch back up to date.

[LeC-D]

Rebased on upstream main (2026-03-28) to bring the branch back up to date.